1. Field of the Invention
The present invention relates to thin-wall tubing generally and, more particularly, to a novel method and apparatus for forming such tubing for later welding of the seam thereof, which method and apparatus economically produce a product having superior quality and in wider ranges of materials, diameters, and thicknesses than heretofore available.
2. Background Art
Thin-wall tubing is useful in a number of applications and is of particular value in the manufacture of metal bellows. Such bellows have utility in such varied applications as pressure and thermal sensors, seals, expansion joints and chambers, and vibration dampeners. The convolutions of the bellows are typically formed by mechanical means from welded thin-wall tubing, after the tubing is formed. Such bellows are manufactured, for example, by Westport Development Manufacturing Company, Inc., Orange, Conn. It will be understood that, in the manufacture of such bellows, it is of critical importance that the weld on the tubing used be strong and that the diameter of the tubing be uniform.
Known methods and apparatus for forming welded thin-wall tubing have a number of substantial limitations, one of which is the relatively high cost of the apparatus. In one type of apparatus, the basic tubing shape is formed from flat strip and the seam is welded by moving the tubing under a fixed welding torch. This type of apparatus relies on the formed tube itself for support, there being no internal support, and, therefore, there is a practical limit to the thinness of the tube. For example, the minimum wall thickness for a 4-inch diameter tube is on the order of 0.020 inch.
In another type of apparatus, the edges of the formed tube are fixedly clamped to a mandrel surface by means of a plurality of fingers and the welding torch is moved along the seam. This type of apparatus has the advantage of being able to weld a variety of shapes, in addition to round tubing, but has as one disadvantage the practical limitation of a relatively short maximum length. Also, the apparatus requires careful adjustment of a "springy" piece of sheet metal to butt the edges perfectly. Too high a clamping pressure will cause the mandrel to bend and too low a clamping pressure will cause the resulting tube to be tapered because it laps over during the welding and cooling process. If supports are added under the mandrel, there is a risk of marking or wrinkling the tube. Typically, the lower dimensional limits on tubes produced with this type of apparatus are 0.0055 wall thickness and 11/4-inch OD.
Neither type of apparatus has the ability to readily handle difficult to weld materials such as Monel and both tend to produce thin-wall tubing having kinks, scratches, and/or dents.
Accordingly, it is a principal object of the present invention to provide a method and apparatus for forming thin-wall tubing which will produce such tubing of wider ranges of wall thicknesses, diameters, and materials than available with conventional methods and apparatus.
Another object of the invention is to provide such method and apparatus which produces such tubing having a uniform diameter and no tapering.
An additional object of the invention is to provide such method and apparatus which produces such tubing of any desired length.
A further object of the invention is to provide such method and apparatus which is relatively economical and easy to use.
Other objects of the invention, as well as particular features and advantages thereof, will, in part, be obvious and will, in part, be apparent from the following description and the accompanying drawing figures.